This invention relates to a turbine, particularly for an exhaust gas turbocharger, having a guide apparatus with a ring of guide vanes that are arranged concentrically around a rotor axis and that are each pivotable between two end limits, which comprises a first securing ring arranged at the side of a bearing housing, in which the guide vanes are each mounted by means of a first trunnion, and in which the guide vanes are each mounted with a second trunnion at the side of a turbine housing, and having an adjusting mechanism for adjusting one of the end limits, wherein the guide vanes are freely pivotable under the influence of flow forces in an angle adjustment range determined by the end limits, and wherein the guide apparatus and the adjusting mechanism form a single subassembly or unit assembly.
West German Patent No. DE-PS 33 25 756 (equivalent to U.S. Pat. No. 4,657,480) describes an exhaust gas turbocharger with guide vanes which are freely pivotable under the influence of flow forces within an angle adjusting range determined by means of end limits. In order to adjust one of the end limits, an adjusting ring is provided which forms a portion of the wall of the flow channel and which has saw tooth form contact surfaces for the free ends of the guide vanes. Within the limits determined in this manner, an automatic adjustment of the guide vanes occurs in accordance with the flow in the partial load range in order to reduce gap losses and impact losses. When the load is increased, the guide vanes position themselves at the largest possible open angle permitted by the position of the end limit. The setting of the end limit takes place in accordance with the charge pressure characteristic. Fabrication and assembly require an expenditure which is not insubstantial. First the guide vanes must be individually inserted with their trunnions in corresponding bore holes in the turbine housing. Only thereafter can the assembly be attached to the turbine housing.
U.S. Pat. No. 4,403,913 discloses an outlet guide apparatus of a compressor in which the air from a compressor wheel is conveyed radially outwardly through the guide apparatus in a spiral diffuser. The guide vanes of the guide apparatus are each mounted at only one side. This technique of mounting the guide vanes can be used in a compressor, since in comparison with an exhaust gas turbine, significantly smaller mechanical and thermal stresses are encountered. A guide apparatus for the turbine of an exhaust gas turbocharger requires two sided mounting of the guide vanes.
U.S. Pat. No. 4,179,247 describes a turbocharger having an adjusting mechanism for the guide vanes. The guide vanes are forcibly guided, and the adjusting mechanism contains a large number of individual component parts which require an expensive construction and a high assembly cost. There exists a danger of disturbances, especially since, due to the high operating temperature, binding and/or displacement or distortion is very difficult to avoid in practice. The adjusting mechanism requires a relatively large amount of space; cooling channels cannot be provided in this region which is subjected to the hot exhaust gases. Further, difficulties arise with regard to achieving a secure sealing of the vane shafts which extend outwardly from the flow channel.